When Tonya Rooks moved into public housing, she paid about $50 for rent. Within 18 months she landed a full-time job as a recruiter with First Things First and chose to pay a flat-rate rent of $447 a month, instead of 30 percent of her income.

A flat rate allowed her to plan her monthly expenses better. With overtime pay, her rent would have fluctuated.

For six months, until she left public housing, she was among 206 residents who earned income but lived in public housing by choice and paid flat-rate rent. The flat rates are close to market rate: tenants living in Greenwood will pay $490 for a two-bedroom apartment; residents at the Villages at Alton Park pay $509 for a two-bedroom unit.

HUD requires housing authorities to offer a flat-rate option, said Betsy McCright, executive director of the Chattanooga Housing Authority. Sometimes the flat rate is less expensive than paying 30 percent of their income.

"When we have working families who choose to stay in public housing we have ... a more mixed-income community," said McCright. "People see what work produces. They see that these families may be able to do more for their children. So we hope they set up as role models for other residents who may not choose to work at a given time."

Other housing authority leaders have said that having flat-rate renters helps the housing authority get more funding from rent than it would renting to people with no income or less income.

But it's still only a small number. Only 105,000 families of the estimated 1.2 million public housing households were identified in HUD's data system as paying either flat rents or ceiling rents.

The largest number of CHA renters paying a flat rate live in College Hill Courts, where a two-bedroom unit is $447. No public housing resident chooses the option in Fairmount, where the flat-rate rent is $802.

McCright said she expects some Fairmount residents eventually to choose the flat-rate option because it is a site where residents are required to work if they want to live there. As their incomes rise, they may choose to remain in the community. Fairmount is the only public housing site north of the Tennessee River where nearby homes range in price from $75,000 to more than $200,000.